1. Field of the Invention
The present invention relates to an antenna element, especially an antenna element for use in base station antennas for mobile communications.
2. Description of the Related Art
Such antenna elements are previously known, e.g., from the U.S. Pat. No. 5,080,961 (Tsao) and an article in Electronic Letters, vol. 30, No. 22, pp. 1814-1815, 1994 (Yamazaki). In order to obtain a relatively broad bandwidth and dual polarisation with a high degree of isolation between the two channels, it has been necessary, hitherto, to arrange an air-bridge in a planar feed network (as proposed by Tsao) or to dispose two different dielectric boards separated by the ground plane layer (as proposed by Yamazaki). These measures involve serious complications in the design process and the manufacture or increased costs because of the two separate dielectric boards with associated feed networks.